The number of coating agent compositions using water but not an organic solvent has been increasing in view of, for example, recent environmental problems. Examples of applications of the coating agent compositions include aqueous paint, aqueous ink, optical coating agents, agents for fibers, and agents for paper. A coating agent composition to be used for such applications has a UV absorber or a light stabilizer such as a radical scavenger added for improving the weatherability of a formed coating film in some cases. However, such light stabilizers have a problem in that, when the light stabilizer is added to an aqueous composition, the blended light stabilizer is not dispersed well, so a formed coating film does not have sufficient weatherability because the light stabilizer is generally an oil-soluble organic compound. The light stabilizers have another problem in that a coating agent composition with the light stabilizer added involves the separation of the light stabilizer during storage of the composition, thereby resulting in poor storage stability.
To cope with the foregoing, in an application where an aqueous emulsion is used, for example, the addition of a light stabilizer when polymerizing the aqueous emulsion has been known. For example, Patent Document 1 discloses an acryl silicone emulsion composition obtained by the emulsion polymerization of a mixture containing: a monomer mixture composed of 30 to 96 wt % (mass %) of a (meth)acrylate monomer (1), 1 to 10 wt % (mass %) of one kind of specific polymerizable carboxylic acid (2) or a mixture of two or more kinds of the carboxylic acids, 1 to 10 wt % (mass %) of a polymerizable emulsifier (3), 1 to 20 wt % (mass %) of a benzophenone- or benzotriazole-based polymerizable light stabilizer (4), and 1 to 30 wt % (mass %) of an organoalkoxysilane compound (5) having at least one glycidyl group in one molecule thereof (the total amount being 100 wt % (mass %)); and 0.1 to 5 wt % (mass %) of a hindered amine-based light stabilizer (HALS) (6) having a base constant (PKb) of 8 or more (claim 1).
In addition, Patent Document 2 discloses an aqueous paint composition containing (A) a fluoroolefin-based copolymer emulsion and (B) a copolymer emulsion containing a UV absorber and/or a light stabilizer obtained by the emulsion polymerization of a mixture of: a monomer mixture composed of (a) 5 to 70 wt % (mass %) of a polymerizable unsaturated monomer having a cycloalkyl group and (b) 30 to 95 wt % (mass %) of any other polymerizable unsaturated monomer; and (c) the UV absorber and/or the light stabilizer (claim 1). In addition, paragraph [0016] of Patent Document 2 discloses a UV absorber such as a salicylic acid derivative or a benzophenone- or benzotriazole-based UV absorber and a light stabilizer such as a hindered amine derivative.
A method involving: emulsifying or dispersing a light stabilizer into water in advance; and adding the resultant to an aqueous emulsion has also been known. For example, Patent Document 3 discloses: a light stabilizer aqueous emulsion containing a light stabilizer, an emulsifier, and water, in which the content of the light stabilizer is 20 to 85 mass % (claim 1); and the light stabilizer aqueous emulsion in which the light stabilizer is a triazine-based UV absorber (claim 3). The light stabilizer aqueous emulsion can be added to an aqueous emulsion or an aqueous coating agent composition later. Therefore, the light stabilizer aqueous emulsion is advantageous in that it has an extremely simple structure and easily exhibits the functions of so-called weatherability.
Patent Document 1: JP 11-080486 A, Claims
Patent Document 2: JP 2002-285045 A, Claims, paragraph
Patent Document 3: JP 2003-261759 A, Claims,